In recent years, widespread use of a color image has been vigorous and hence a demand for an improvement in image quality is growing. In a digital full-color copying machine or printer, a color image original is subjected to color separation with respective filters of blue, green, and red colors, and then latent images corresponding to the original image are developed with respective developers of yellow, magenta, cyan, and black colors. Accordingly, a colorant in the developer of each color largely affects the image quality. In general, upon dispersion of a pigment in any one of the various media, it is difficult to make the pigment sufficiently fine or to uniformly disperse the pigment. In the production of a paint, an ink, a color filter, a resin molded article, or the like, a pigment dispersant has been utilized as an additive for reducing the particle diameter of a pigment to cause the pigment to sufficiently exert its performance as a coloring material (such as coloring power, transparency, or gloss).
A color filter is indispensable to enable a liquid crystal display to display a color and is hence an important part that determines the performance of the liquid crystal display. A dyeing method, a printing method, an inkjet method, a photoresist method, or the like has been known as a conventional method of producing the color filter. Of those, the photoresist method has become a mainstream production method in recent years because of the following reasons. The method facilitates the control and reproduction of spectral characteristics, and provides so high a resolution as to be capable of additionally high-definition patterning.
A pigment has been generally used as a colorant in the photoresist method. However, it has been known that the pigment involves a depolarization action (collapse of polarization) owing to its certain particle diameter, thereby reducing the contrast ratio of the color display of the liquid crystal display. In addition, in a system using the pigment, it is difficult to obtain high permeability for backlight and hence the extent of an improvement in brightness of the color filter is limited. Further, the pigment is insoluble in an organic solvent or a polymer. Accordingly, a colored resist composition is obtained as a dispersed product but it is difficult to stabilize the dispersion. In contrast, a dye is generally soluble in an organic solvent or a polymer and is hence stable even in a colored resist composition without causing agglomeration. Accordingly, a color filter obtained from a resist composition using the dye as a colorant is free of any depolarization action because the dye is being dispersed at a molecular level, and the color filter is excellent in permeability for backlight. A red color filter using C.I. Acid Red 6 that is a monoazo-based coloring matter has been reported so far because the filter has good spectral characteristics and enables image display with a high display contrast ratio (see PTL 1). As migration to broadband progresses, an image with an additionally high definition needs to be displayed. In view of the foregoing, the development of an additive for reducing the particle diameter of a pigment to cause the pigment to sufficiently exert its performance as a coloring material (such as coloring power, transparency, or gloss) has been strongly demanded in order that good spectral characteristics and a high contrast ratio can be realized.